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Networking & Internet

Checking Your Network Interface

Linux uses ifconfig to view and configure network interfaces. Your ethernet card will usually appear as eth0, a loopback as lo. 

# ifconfig
eth0  Link encap:Ethernet  HWaddr 00:0C:29:AB:CD:EF
      inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

lo    Link encap:Local Loopback
      inet addr:127.0.0.1  Mask:255.0.0.0
      UP LOOPBACK RUNNING  MTU:16436  Metric:1

Ethernet (LAN) Setup

If you have a DHCP server on your network (most home routers do), getting online is simple:

# dhclient eth0    # request an IP via DHCP
# ping -c 4 8.8.8.8   # test internet connectivity

For a static IP, edit /etc/network/interfaces (Debian) or /etc/sysconfig/network-scripts/ifcfg-eth0 (Red Hat).

Dial-Up Internet (PPP)

Dial-up was still common in 2000. Linux uses PPP (Point-to-Point Protocol) to connect via modem. Most distributions include a GUI dialler:

  • kppp — KDE's PPP dialler, very user-friendly.
  • gnome-ppp — GNOME equivalent.
  • wvdial — command-line dialler that auto-detects your modem.
  • pppconfig + pon/poff — Debian's approach.
# wvdial &          # dial up using wvdial.conf settings
# pon provider      # Debian: bring up PPP link
# poff provider     # Debian: drop PPP link

DNS Configuration

DNS servers are configured in /etc/resolv.conf:

nameserver 8.8.8.8
nameserver 8.8.4.4
search localdomain

Host-to-IP overrides can be added in /etc/hosts. The order in which DNS and local files are consulted is controlled by /etc/nsswitch.conf.

Useful Networking Commands

$ ping hostname        # test connectivity
$ traceroute hostname  # trace route to host
$ netstat -rn          # show routing table
$ nslookup domain.com  # query DNS
$ route -n             # show routing table (alt)
# ifconfig eth0 up     # bring interface up
# ifconfig eth0 down   # bring interface down

Internet Tools

Once connected, check out our Internet Tools and Network Connectivity & Security Tools sections for browsers, email clients, IRC, and more.